Thornback Guitarfish

Fascinating facts about the Thornback Guitarfish

• A 1880 paper by Jordan and Gilbert named the species triseriata, literally “three rows,” after the trio of thorn lines that run from the middle of its back onto the tail – a living reference guide for anyone spotting it in the sand. This tiny anatomical detail sets it apart from true guitarfishes and hints at its deeper evolutionary ties to electric rays. It reminds us how a single trait can rewrite a whole family tree.
• Even though it looks like a ray, DNA studies show the thornback guitarfish is actually the sister group to electric rays, not to the guitarfishes it mimics. This surprise reshapes our picture of the Myliobatiformes order, proving that outward shape can be a misleading disguise.
• The ray spends most of its daylight hours half-buried in mud or sand in water shallower than 6 m (20 ft), yet it can dive as deep as 137 m (449 ft) when needed. Its ability to switch habitats so dramatically demonstrates a flexibility that helps it survive in the ever-changing coastal zones.
• Females give birth to anywhere from 1 to 15 pups each August after a roughly year-long gestation, and the newborns are already 11 cm (4.3 in) long. That wide litter range shows how the species balances low-predation environments with the need to keep numbers steady.
• During the day the ray uses its ampullae of Lorenzini to sniff out prey, tuning into electric fields between 5 and 15 Hz – the same range many small crustaceans emit. This electro-sense lets it hunt hidden worms and shrimp in the murky bottom, highlighting a sensory world far beyond human sight.

At a glance

About the Thornback Guitarfish

The thornback guitarfish (Platyrhinoidis triseriata) glides through the shallow bays of the northeastern Pacific, its heart-shaped pectoral disc a muted olive-gray that blends seamlessly with the sand and kelp. Growing up to 91 cm (36 in), it is instantly recognizable by three parallel rows of large, hooked thorns that begin at the middle of its back and trail onto the robust tail, which bears two dorsal fins and an almost elliptical caudal fin. Its short, broad snout and small, widely spaced eyes sit above spiracles larger than the eyes themselves, while the mouth, lined with 68–82 upper and 64–78 lower tooth rows, opens to a wide, gently arched gape. By day it often buries itself partially in mud or sand, emerging to hunt polychaete worms, crabs, shrimps, isopods, squids and small bony fishes such as anchovies and surfperches, detecting prey with electroreceptive ampullae tuned to 5–15 Hz. A surprising trait is its aplacental viviparity: females carry a single yolk sac, giving birth to 1–15 pups each August after a roughly year-long gestation, the newborns measuring about 11 cm (4.3 in). In the coastal waters from Tomales Bay to Magdalena Bay, and in isolated Gulf of California pockets, these rays form seasonal aggregations in bays and sloughs, sometimes gathering in large groups that vanish as the tide recedes. Though modest in size, they are prey for sharks and the northern elephant seal (Mirounga angustirostris), and they host parasites like the tapeworm Echinobothrium californiense and the nematode Proleptus acutus. Their modest, docile nature makes them a favorite in public aquariums, where visitors can watch the subtle sway of their dorsal fins and the graceful flick of their caudal fin as they navigate the benthic realm.

More fish to discover

Browse Feravox